This invention relates to a blackbody radiation source operable at low temperatures.
Sensors such as imaging focal plane array sensors are calibrated prior to, and sometimes during, service. In one calibration procedure, the sensor is placed into a facing relation with a calibration source which produces a standard condition. The standard condition typically includes a simulated background field comparable with the background field expected in service for the wavelength range of the sensor but without any target present. The sensor is operated while facing the calibration source. From the data collected in the calibration procedure, the operability of, zero values for, and/or scaling factors for individual pixel sensor elements of the array are determined and stored for later use.
An important class of sensors includes infrared sensors for use in space or in viewing space from earth. The relevant background for the calibration of such sensors is a blackbody radiation source having a low temperature of 200.RTM.K. or less. One blackbody radiation source previously used for this calibration procedure has been a bath of liquid nitrogen or a flat metal container whose exterior is painted black and which is filled with liquid nitrogen. This type of source yields somewhat unpredictable equivalent radiometric temperatures. Reflections from the ambient environment may interfere with the measurement of the source. Additionally, this source is limited to a single source temperature and lacks the flexibility required for many applications.
There is a need for an improved low-temperature blackbody radiation source for use in calibrating sensors and in other applications. The present invention fulfills this need, and further provides related advantages.